The purpose of this proposal is to investigate three separate problems on hemispheric brain lateralization in man: (1) the nature and degree of hemispheric speech representation in non-right-handers; (2) developmental parameters of hemispheric speech lateralization in left- and right-handed children and (3) developmental parameters of hemispheric speech lateralization in childhood dyslexia. Problem I will examine this relatioship in a large group of normal high school students (left- and right-handers) who are further classified on familial handedness (i.e., familial sinistrality) and strength of manual dexterity. Estimates of hemispheric speech representation will then be made on the basis of cross-modal asymmetry measures in audition (dichotic stimulation) and vision (visual half-field stimulation). Perceptual tests will also be administratered to determine whether Gestalt-perceptive ability varies as a function of the preceding variables within and between groups. Problem II will investigate the development of speech brain lateralization in both normal left- and right-handed children using the dichotic stimulation procedure. The left-handed children (N=60) will be selected from a large ongoing longitudinal study in which repeat measures of manual laterality and hemispheric speech laterality are available at ages 5, 8 and 11. Problem III will examine similar measures in dyslexic and matched control readers at the same ages. also, cross-sectional studies will be run to determine whether possible floor effects in the dichotic stimulation technique may be confounding the onset of the ear asymmetry at younger ages (Problems II and III). This problem has not been investigated before. Utilization of normal Ss who are not brain-injured is proposed in order to avoid the confounding effects of motor and sensory deficits in brain-injury patients whose lesion specificity is often unclear.